The present invention relates to aerated ultra low density cast-dehydrated detergent bars. The invention particularly relates to a process for preparing aerated ultra low density cast-dehydrated detergent bars wherein the air is entrained in the bars after rigidification and shaping the product.
Soap or non-soap detergent articles are traditionally produced by shear working/homogenisation of the formulation followed by extrusion and stamping. This procedure is only suitable for detergent bar formulations which are thermoplastic or which are not shear sensitive. The formulations that are shear sensitive are generally produced by the process of casting. In the manufacture of detergent compositions by casting the formulated system is taken to a fluid state by raising the temperature, filled into moulds, and cooled.
The water content in the detergent bars is generally maintained around 5-40%. If gases such as air can be entrapped in the detergent bar the bulk density of the bar can be reduced and it enables the manufacture of larger size bars for a given weight. It is also possible to entrap sufficient air in order to make the bars float in the washing solution. The concept of entrapment of air or gas has been achieved more particularly for soap bars as it is an advantage to have the bars float in the bath tub.
U.S. Pat. No. 2,295,594 (PandG, 1942) discloses a process for obtaining floating soap comprising mechanical air entrapment through whipping and extrusion of soap in a condition of pasty cohesiveness such that air in finely divided bubble form can be incorporated. The bars are allowed to cool and harden after extrusion. The soap bar compositions do not contain any non-soap detergent active.
U.S. Pat. No. 5,972,860 (Kao Corporation, 1999), discloses aerated detergent bar essentially incorporating inorganic salts and/or polyols and non-ionic surfactants wherein the air is in the fine bubble form and is entrapped in the formulation before casting.
U.S. Pat. No. 5,194,172 (PandG, 1990) discloses an aerated freezer bar comprising fatty acid soap, sucrose, hydrophobic material selected from waxes, and water.
U.S. Pat. No. 5,219,487 (PandG, 1992) discloses an aerated freezer soap bar comprising fatty acid soap, free fatty acid, salt, and water.
The prior art generally teaches compositions and manufacture of aerated soap bars wherein air entrapment in fine bubble form prior to rigidification and shaping of the product is essential. Air entrapment prior to shaping limits the formulation flexibility and requires special purpose equipment to provide mechanical agitation for whipping in air that makes the process capital intensive. The amount of air entrapped is also low and thus detergent bars with ultra low density can not be obtained. It has now been possible to obtain ultra low density cast-dehydrated bars comprising fatty acid soap, non soap detergent active, and very high amount of air, wherein the air is entrained in to the bars after rigidification and shaping of the product. This technology provides formulation flexibility and results in ultra low-density bars that can be produced economically.
According to one aspect of the present invention there is provided an ultra low density cast-dehydrated detergent bar composition comprising:
i 10-60% by volume a neutralised carboxylic fatty acid with chain length C8-C24,
ii 0-40% by volume non-soap surfactant, and
iii 1-90% by volume air
According to a preferred aspect of the invention the said neutralised carboxylic fatty acid comprises at least 50% saturated fatty acid with C16-C24 chain length, more preferably 70% is a saturated fatty acid with C16-C20 chain length and the said non-soap surfactant is at least 1% and up to 40%.
In the formulation it is particularly preferred that the ratio of soap to non-soap detergent active is greater than 0.5.
According to another aspect of the present invention there is provided a process for preparing an ultra low density cast-dehydrated detergent bar comprising the steps of:
i. heating a mixture comprising (a) 10-60% by weight a neutralised carboxylic fatty acid with chain length C8-C24, (b) 0-40% by weight non-soap surfactant, and (c) 1-90% by weight water, to a temperature in the range 50-100xc2x0 C. to obtain a pourable melt,
ii. pouring the said melt into a mould,
iii. cooling the melt to bring about rigidification, and
iv. dehydrating the rigid bar to bring down the moisture level to enable entrainment of air in the range 1-90% by volume of the composition.
Preferably the density of the detergent bars of the invention is less than 0.9 g/cc, more preferred less than 0.8 g/cc, even more preferred from 0.25 to 0.70 g/cc